Packet-switched networks, such as networks based on the TCP/IP protocol suite, can distribute a rich array of digital content to a variety of client applications. One popular application is a personal computer browser for retrieving documents over the Internet written in the Hypertext Markup Language (HTML). Frequently, these documents include embedded content. Where once the digital content consisted primarily of text and static images, digital content has grown to include audio and video content as well as dynamic content customized for an individual user. Additionally, digital content can include updates such as software and programming updates.
Unicast protocols offer point-to-point communication between a server and a client that can be used for delivering content. Unicast communications can be connection-oriented or connectionless. For connection-oriented unicast protocols, each request for content can result in the establishment of a connection between the server and the client. Maintaining the connection requires the server to dedicate the resources needed to provide the content to the client. For connectionless unicast communications, the server can send an amount of data towards the client without establishing a connection between the client and the server. While a connectionless unicast communication can avoid the overhead of establishing the connection and the need to reserve resources for the connection, the connectionless unicast communication may not provide a mechanism for ensuring delivery of the content.
In contrast to unicast protocols, multicast protocols can allow substantially simultaneous distribution of digital content to a large number of clients without creating multiple point-to-point connections. The server can provide the content to a multicast group with each member of the multicast group receiving a copy of the content at substantially the same time. Generally, multicast communications require network resources to replicate the content as it traverses the network and to maintain information regarding which clients are receiving the multicast content in order to ensure content is replicated throughout the network correctly.
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